In this study, first we reviewed several studies on social cost-benefit approach in the field of road network research as well as procedure of road funding and optimal level of road building. According to the comprehensive study conducted by Dr.Greene and his colleagues, social costs incurred by transport, especially road transport, should cover non-monetary personal (driving), monetary private (purchase of a car), bundled monetary private (parking), governmental (road maintenance), monetary external (congestion), and non-monetary external (air pollution) costs. We basically followed the categories proposed by Dr.Greene's.Second, we selected Sendai City as our study area. We applied our software and social cost-benefit approach to actual situation in Sendai City and studied the optimal level of road building. We found that the share of the environmental costs out of the total social costs was not high as compared with time cost. We also evaluated the balance among travel demand, existent road network, and road fund required.Third, we analyzed the distribution of the cost of road traffic noise pollution. We evaluated the effectiveness of several policies such as road pricing and road building. Finally we studied the appropriate balance between he level of road network and the source of road fund, and proposed the directions of further studies.